1. Field of the Invention
This invention relates to circuits for offsetting impedance effects in an electric circuit; and it relates, in particular, to a negative conductance network for that purpose.
2. Description of the Prior Art
Negative impedance converters and negative impedance boosters are known in the art for controlling circuit losses of various kinds. They often are inserted in series in a circuit path, but in some versions they are also shunted across the signal path. These prior art circuits usually are subject to at least one of a number of types of problems. For example, they display a nonlinear negative impedance characteristic, and they have a comparatively narrow voltage range in which they are effective as a negative impedance. To reduce the influence of the nonlinearity over a voltage range suitable for practical operation, a voltage supply that is three or four times as large as the operation range must be employed.
Such prior art circuits also usually are highly sensitive to temperature effects and to variations in power supply voltage. In addition, many also depend upon the compensated circuit as a source of operating potential for the compensating circuit. These difficulties make the prior art negative impedance circuits of only very limited value in communication systems wherein it is necessary to effect substantially precise control of current level. One example of such a system would be a private branch exchange having a time division multiplexed conference circuit to which a large number, e.g., 6 to 15, of conferees could be simultaneously connected.